Action Points

Note that the sugar galactose-a-1,3-galactose (alpha-gal) has been well known as an immunologic barrier to animal-human organ transplantation, but wasn't suspected as an allergen because IgE-mediated allergies nearly always involve a protein.

All but two of the 39 patients with a documented clinical history of meat allergy and immunoglobulin E (IgE) against the sugar galactose-a-1,3-galactose (alpha-gal) found in beef, lamb, pork, and other mammalian meats had IgE sensitization to ticks as well.

All but two (95%) also had an A or O blood type, which was higher than the expected 82% rate of B-negative blood type within the general Swedish population, Marianne van Hage, MD, PhD, of the Karolinska Institutet and University Hospital in Stockholm, and colleagues found.

Alpha-gal "is a major blood group substance of nonprimate mammals and is structurally related to blood group B," they explained in a research letter in the December issue of the Journal of Allergy and Clinical Immunology.

While that sugar has been well known as an immunologic barrier to animal-human organ transplantation, it wasn't suspected as an allergen because IgE-mediated allergies nearly always involve a protein.

"Over the past few years, allergy to mammalian meat has been identified as a new syndrome of food allergy presenting as symptoms of delayed severe allergic reactions after consumption of red meat (beef, lamb, or pork)," van Hage's group noted.

The initial cetuximab research pinpointed the lone star tick (Amblyomma americanum) found in the southeastern U.S. as a sensitization culprit, and several reports have confirmed the same is true in red meat allergy.

But the allergy doesn't appear to be limited to the southeastern states.

"We have recently identified alpha-gal in the gastrointestinal tract of the European tick Ixodes ricinus, which provides further evidence of the tick as an initiator of red meat allergy," van Hage and colleagues explained.

They examined all 39 patients seen at a Stockholm allergy clinic who reported delayed allergic reactions after eating red meat and were subsequently found to have IgE to alpha-gal using the ImmunoCAP assay.

All but two patients described delayed symptoms. While urticaria was the most common, 45% of the patients had experienced anaphylaxis.

All patients had IgE against beef, pork, or other alpha-gal sources; most also had IgE to cow's milk, dog, cat, and moose.

In detailed questionnaires, all patients reported having been bitten by ticks, typically more than 10 times.

All but two of the 39 patients tested positive for sensitization to the European I. ricinus tick, with IgE levels strongly correlated to those against alpha-gal.

More than a third of the patients also showed IgE reactions, albeit at lower levels, to the Americantick. Further experiments showed that the two tick species "share similar allergen epitopes but that they also have species-specific epitopes."

For a look at how common alpha-gal reactions were in other populations, the researchers also screened blood from 143 healthy blood donors in the greater Stockholm area, where tick bites are common, and from 207 patients with confirmed Lyme disease from recent tick bites.

As many as 10% showed IgE antibodies to alpha-gal in that general Stockholm population and 22% did in the tick-borne infection group.

IgE levels high enough to be considered alpha-gal sensitization were more common in the Lyme disease group, though (22% versus 3%, P=0.005), "which strengthens the role of tick bites for the induction of IgE to alpha-gal."

UPDATE: This article, originally published Dec. 2, 2013, at 5:34 p.m., was updated with new material (Dec. 3, 2013, at 7:30 p.m.).

The study was supported by research grants from the Swedish Research Council; the Stockholm County Council; the Swedish Heart-Lung Foundation; the Center for Inflammatory Diseases, Karolinska Institutet; the Swedish Asthma and Allergy Association's Research Foundation; the Swedish Cancer and Allergy Foundation; the Konsul Th C Bergs Foundation; the King Gustaf V 80th Birthday Foundation; the Hesselman Foundation; and Karolinska Institutet.

Van Hage reported having received grants from the Swedish MRC, the Swedish Heart-Lung Foundation, the Stockholm County Council Research Fund, and the Swedish Asthma and Allergy Association's Research Foundation, and having received fees for lectures from Thermo Fisher Scientific, Novartis, and ALK-Abello.

Reviewed by Robert Jasmer, MD Associate Clinical Professor of Medicine, University of California, San Francisco and Dorothy Caputo, MA, BSN, RN, Nurse Planner

MedPageToday is a trusted and reliable source for clinical and policy coverage that directly affects the lives and practices of health care professionals.

Physicians and other healthcare professionals may also receive Continuing Medical Education (CME) and Continuing Education (CE) credits at no cost for participating in MedPage Today-hosted educational activities.